1. Field of the Invention.
This invention relates to rocket motors in which hydroxy terminated polybutadiene bound solid propellant grains and silicone rubber insulation are used. More particularly, this invention relates to the prevention of migration of isocyanate curatives from a hydroxy terminated polybutadiene bound propellant grain into a silicone rubber insulator.
2. Description of the Prior Art.
It is well known to use hydroxy terminated polybutadiene as a binder for solid rocket propellant grains. It is also well known to use isocyanates to cure hydroxy terminated polybutadiene.
It has recently become known that silicone rubber is an excellent insulator for rocket motors utilizing solid rocket propellant grains. However, when silicone rubber is utilized as an insulator in rocket motors containing isocyanate cured hydroxy terminated polybutadiene, problems arise. The problems stem from the fact that the isocyanate curatives tend to migrate from the propellant grain into the silicone rubber insulation. When this happens, an undercured surface layer of the propellant results. This undercured surface area represents a zone of weakness and, when the rocket motor is fired, the propellant grain, because of this zone of weakness, would separate from the silicone rubber insulation. When this occurs, a motor blowup is a common result. Ordinarily, excess isocyanate would be added to the rocket motor insulation to prevent isocyanate migration from the propellant grain. This is not possible with silicone rubber insulation.